Patent GB-793633-A (GB)
Title: A method for removing sludges from tanks and for recovering oil from these sludges
Inventor: DIXON ARNOLD GRAHAM
IPC: B63B57/02
Filed: 1955-06-06
Abstract: A method for removing sludge from one or more oil transport tanks and for recovering the oil from this sludge comprises forming the sludge present in one of the tanks into a suspension in a solution in sea-water (or equivalent) of from 0.05 to 0.20 per cent by weight of secondary alkyl sulphates of ammonium or an alkali metal, removing this suspension from the tank and allowing it to stratify, recycling all or part of the resulting aqueous layer to the tank or another of the tanks for the purpose of treating sludge present therein, and maintaining the resulting emulsified layer at a temperature such that it breaks and forms an aqueous layer and a supernatant oil layer. The sea-water solution may contain also water-soluble surface-active agents, free ammonia, sodium sulphate, sodium silicate, magnesium sulphate or calcium chloride.  The secondary alkyl sulphates preferably contain at least 8 (e.g. 10 to 20) carbon atoms per molecule. The solution may be pumped at pressures ranging from 100 to 180 lb. per square inch into the sludge from fixed orifices, manually-controlled hoses, or rotating nozzle devices which may turn slowly in horizontal and vertical planes so that their position changes continually with each revolution.  Alternatively the sludge may be converted into a suspension in the sea-water solution by stirring or by air jets placed beneath the surface. Further quantities of the secondary alkyl sulphates may be added to the recycled aqueous layer.  In an example a commercial product containing sodium secondary alkyl sulphates was dissolved in sea-water in a wash-tank and the solution heated to, and maintained at, 140 DEG  F.  Solution was withdrawn from the bottom of the tank, further heated to 180 DEG  F. and sprayed at 180 lb. per square inch on to sludge in a transport tank.  The resulting suspension was drawn from the bottom of the transport tank and passed into the wash-tank. The lower aqueous layer in the wash-tank was recycled and the process continued, the whole suspension being eventually removed to the wash-tank where, after six hours, the emulsified layer adjacent to, and below, the uppermost (oil) layer broke to form an upper oil layer and a lower aqueous layer.  In a modification the sea-water solution was used at ambient temperature and the emulsified layer which formed in the wash-tank was continuously drawn off to a separating tank where it was heated to a temperature of 160 DEG  F. by steam coils surrounding the tank; the emulsified layer broke to form oil and aqueous layers after 30 minutes.ALSO:A method for removing sludge from one or more oil transport tanks and for recovering the oil from this sludge comprises forming the sludge present in one of the tanks into a suspension in a solution in sea-water (or equivalent) of from 0,05 to 0,20 per cent. by weight of secondary alkyl sulphates of ammonium or an alkali metal, removing this suspension from the tank and allowing it to stratify, recycling all or part of the resulting aqueous layer to the tank or another of the tanks for the purpose of treating sludge present therein, and maintaining the resulting emulsified layer at a temperature such that it breaks and forms an aqueous layer and a supernatant oil layer. The sea-water solution may contain also water-soluble surface-active agents, free ammonia, sodium sulphate, sodium silicate, magnesium sulphate or calcium chloride.  The secondary alkyl sulphates preferably contain at least 8 (e.g. 10 to 20) carbon atoms per molecule.  The solution may be pumped at pressures ranging from 100 to 180 lbs. per square inch into the sludge from fixed orifices, manually-controlled hoses, or rotating nozzle devices which may turn slowly in horizontal and vertical planes so that their position changes continually with each revolution.  Alternatively the sludge may be converted into a suspension in the sea-water solution by stirring or by air jets placed beneath the surface.  Further quantities of the secondary alkyl sulphates may be added to the recycled aqueous layer.  In an example a commercial product containing sodium secondary alkyl sulphates was dissolved in sea-water in a wash-tank and the solution heated to, and maintained at 140 DEG F.  Solution was withdrawn from the bottom of the tank, further heated to 180 DEG F. and sprayed at 180 lbs. per square inch onto sludge in a transport tank.  The resulting suspension was drawn from the bottom of the transport tank and passed into the wash-tank.  The lower aqueous layer in the wash-tank was recycled and the process continued, the whole suspension being eventually removed to the wash-tank where, after six hours, the emulsified layer adjacent to, and below, the uppermost (oil) layer broke to form an upper oil layer and a lower aqueous layer.  In a modification the sea-water solution was used at ambient temperature and the emulsified layer which formed in the wash-tank was continuously drawn off to a separating tank where it was heated to a temperature of 160 DEG F. by steam coils surrounding the tank; the emulsified layer broke to form oil and aqueous layers after 30 minutes.